Currently, current transformers used in a power grid proportionally reduce a large current in the primary circuit to a small current required in a secondary measurement circuit, mainly achieving electric isolation between the high voltage end and low voltage end and proportional measurement. The metering current transformer is one of main metering instruments for trade settlement in the power grid, and falls into scope prescribed in the mandatory test specifications of China. Each metering current transformer can only be put into normal use after being verified to be qualified by passing the initial examination and the periodic examinations. With rapid development of economy, both the increment and the holding of the metering current transformers have grown sharply. The traditional manual examining method, due to problems such as low working efficiency, labor-intensive and intervening to examining results by manual wire connecting, can not fulfill the increasing demand for examining transformers any more, thus it is necessary to develop a system for examining current transformers full-automatically.
In a conventional device for examining transformers, a semi-automatic working mode is adopted, wire connecting and disconnecting are performed manually, and the examining device performs the basic error examinations automatically. However, insulation tests, such as the insulation resistance test, the withstand voltage test, the inter-turn insulation test and the magnetic saturation margin test, are all required to be performed manually, so the working efficiency is rather low, and some examinations even can not be performed owing to the limitation of the capacity of the examining devices.
Low-voltage current transformers are divided into two types: bus-type (bus mode) current transformers and multi-turn-type (multi-turn mode) current transformers. The primary winding connecting methods for the two types of current transformers are different and external dimensions, diameters and positions of center-holes for bus-type current transformers of different transformation ratios are different, thus the system for examining current transformers needs to meet the requirement of different wire connecting modes and different dimensions from bus-type current transformers and multi-turn-type current transformers. A single conventional device for examining current transformers full-automatically can not fulfill the demand for examining huge numbers of transformers, and do not have the advantages of automatic production line, hence integration of multiple devices for examining current transformers is required in the system for examining transformers.
To sum up, it is significant to develop a system for examining current transformers full-automatically, which is adapted for bus-type current transformers and multi-turn-type current transformers, and is an integration of multiple examining devices and a conveying line.